Golf ball manufacturers are continuously changing and improving golf ball design such as by improving overall ball construction or by developing better materials for one or more layers of the ball. At one time, for instance, many manufacturers made golf balls with liquid-filled cores surrounded by elastic windings. This construction was preferred by advanced golfers who wanted a soft feel from the ball.
At the time, golf balls having a solid core construction were often perceived to be inferior at least because of the hard feel of the ball when struck by a club. Softer core materials were available to provide a softer feel, but only at the expense of lowering the coefficient of restitution (COR) of the core. As the COR of a golf ball decreases, the distance a ball travels likewise decreases. Thus, wound golf balls remained a popular ball construction until improvements in solid core materials.
More recently, however, there have been many advancements in solid core design that have played a part in the growing trend toward making solid core golf balls. For example, new developments in core materials have resulted in the ability to make solid cores with lower compression values so that they feel softer when struck with a club while reducing or eliminating the loss of COR previously seen in lower compression core materials.
Typically, solid core layers are made of highly resilient, elastic material, such as polybutadiene. As discussed above, conventional solid core compositions typically resulted in the core having a high compression, which made the ball feel hard when struck by a club. In fact, a high compression core is less likely to deform or deflect under pressure. As compression is lowered, the ball feels softer and is more prone to deform or change under pressure or impact forces. This additional “give” makes the core feel softer.
Traditionally, achieving this softer feel for a solid golf ball came at the expense of reduced COR. Recent developments in core materials, however, have enabled golf ball manufacturers to use materials having lower compression values while still achieving desired ball COR. In the past, it was not possible to obtain both a soft feel and acceptable COR.
Today, many golf ball manufacturers use solid core constructions in favor of wound ball constructions. The cores may be made of a single layer of material or may be formed from two or more layers of material.
Once the solid core is formed, additional layers of material may be formed around it by a wide variety of molding processes. Some examples of molding processes that might be used include injection molding, compression molding, casting, reaction injection molding, and the like. Many of these molding processes utilize high pressure to form a layer of material around a golf ball component. For instance, an injection molding process typically involves placing a golf ball component in a molding cavity and injecting layer material around the component under high pressure. Usually, the injection molded material is injected into the cavity around the core at a plurality of locations such that the material simultaneously exerts a force on the core at each location. Injection continues until the material covers the core and solidifies.
As the compression value of the core becomes lower, however, the core becomes more susceptible to deformation during molding. This deformation results in a non-uniform thickness of the molded layer. In the past, this phenomenon was not a significant factor to consider when molding around a solid core for at least two reasons.
First, the need for high compression materials in order to form cores with an acceptable COR meant that the core was much more resistant to deformation during molding of surrounding layers. As a result, the high compression core was less likely to deform significantly during the injection molding process.
Second, in the past the injection molded layer material often was relatively thick, i.e., about 0.080 inches for a “standard” cover layer and about 0.065 inches thick for a “thin” layer. Thus, any deformation exhibited by the core during molding would not result in a significant percentage variation in layer thickness. Moreover, skilled artisans avoided the practical difficulties of obtaining suitable layer thickness uniformity from injection molding thin layers simply by not making golf balls with thin layers.
Today, the trend in the golf ball industry is to use solid core materials having lower compression values and to mold one or more substantially thinner layers around it. In other words, both factors described above that helped mask the phenomenon of core deformation during molding additional layers under pressure no longer apply. Some golf balls with solid core constructions use core materials having low compression. Additionally, many ball constructions utilize considerably thinner molded layers than previously used in golf ball manufacturing. The injection molded casing, or inner cover layer, of the Titleist Pro V1, for instance, is 0.035 inches thick. Additionally, the use of larger diameter cores than used in the past also has led to thinner cover or intermediate layers.
As these design parameters push further toward even lower compression core materials and even thinner molded layers, however, the phenomenon of non-uniform molded layer thickness may become increasingly more significant because a softer, more elastic core will deflect more under the substantial pressure exerted on it during injection molding. The differences in layer thickness also can result in a considerable lack of uniformity on a percentage basis when the molded layer is thin. This percentage difference may become even more apparent as the desired thickness of the molded layer decreases.
In view of the current popularity in solid core constructions using materials with low compression values as well as the trend toward molding thin layers around the core, a continuing need exists for a reliable and efficient method of molding thin layers of material around a golf ball core or golf ball component having a low compression such that the molded layer has improved layer thickness uniformity.